1. Field of the Invention
The invention relates to computer data networks, and more particularly, to network file server architectures for computer networks.
2. Description of the Related Art
Over the past ten years, remarkable increases in hardware price/performance ratios have caused a startling shift in both technical and office computing environments. Distributed workstation-server networks are displacing the once pervasive dumb terminal attached to mainframe or minicomputer. To date, however, network I/O limitations have constrained the potential performance available to workstation users. This situation has developed in part because dramatic jumps in microprocessor performance have exceeded increases in network I/O performance.
In a computer network, individual user workstations are referred to as clients, and shared resources for filing, printing, data storage and wide-area communications are referred to as servers. Clients and servers are all considered nodes of a network. Client nodes use standard communications protocols to exchange service requests and responses with server nodes.
Present-day network clients and servers usually run the DOS, Macintosh OS, OS/2, or Unix operating systems. Local networks are usually Ethernet or Token Ring at the high end, Arcnet in the midrange, or LocalTalk or StarLAN at the low end. The client-server communication protocols are fairly strictly dictated by the operating system environment--usually one of several proprietary schemes for PCs (NetWare, 3Plus, Vines, LANManager, LANServer); AppleTalk for Macintoshes; and TCP/IP with NFS or RFS for Unix. These protocols are all well-known in the industry.
Unix client nodes typically feature a 16- or 32-bit microprocessor with 1-8 MB of primary memory, a 640.times.1024 pixel display, and a built-in network interface. A 40-100 MB local disk is often optional. Low-end examples are 80286-based PCs or 68000-based Macintosh I's; mid-range machines include 80386 PCs, Macintosh II's, and 680X0-based Unix workstations; high-end machines include RISC-based DEC, HP, and Sun Unix workstations. Servers are typically nothing more than repackaged client nodes, configured in 19-inch racks rather than desk sideboxes. The extra space of a 19-inch rack is used for additional backplane slots, disk or tape drives, and power supplies.
Driven by RISC and CISC microprocessor developments, client workstation performance has increased by more than a factor of ten in the last few years. Concurrently, these extremely fast clients have also gained an appetite for data that remote servers are unable to satisfy. Because the I/O shortfall is most dramatic in the Unix environment, the description of the preferred embodiment of the present invention will focus on Unix file servers. The architectural principles that solve the Unix server I/O problem, however, extend easily to server performance bottlenecks in other operating system environments as well. Similarly, the description of the preferred embodiment will focus on Ethernet implementations, though the principles extend easily to other types of networks.
In most Unix environments, clients and servers exchange file data using the Network File System ("NFS"), a standard promulgated by Sun Microsystems and now widely adopted by the Unix community. NFS is defined in a document entitled, "NFS: Network File System Protocol Specification," Request For Comments (RFC) 1094, by Sun Microsystems, Inc. (March 1989). This document is incorporated herein by reference in its entirety.
While simple and reliable, NFS is not optimal. Clients using NFS place considerable demands upon both networks and NFS servers supplying clients with NFS data. This demand is particularly acute for so-called diskless clients that have no local disks and therefore depend on a file server for application binaries and virtual memory paging as well as data. For these Unix client-server configurations, the ten-to-one increase in client power has not been matched by a ten-to-one increase in Ethernet capacity, in disk speed, or server disk-to-network I/O throughput.
The result is that the number of diskless clients that a single modern high-end server can adequately support has dropped to between 5-10, depending on client power and application workload. For clients containing small local disks for applications and paging, referred to as dataless clients, the client-to-server ratio is about twice this, or between 10-20.
Such low client/server ratios cause piecewise network configurations in which each local Ethernet contains isolated traffic for its-own 5-10 (diskless) clients and dedicated server. For overall connectivity, these local networks are usually joined together with an Ethernet backbone or, in the future, with an FDDI backbone. These backbones are typically connected to the local networks either by IP routers or MAC-level bridges, coupling the local networks together directly, or by a second server functioning as a network interface, coupling servers for all the local networks together.
In addition to performance considerations, the low client-to-server ratio creates computing problems in several additional ways:
1. Sharing. Development groups of more than 5-10 people cannot share the same server, and thus cannot easily share files without file replication and manual, multi-server updates. Bridges or routers are a partial solution but inflict a performance penalty due to more network hops.
2. Administration. System administrators must maintain many limited-capacity servers rather than a few more substantial servers. This burden includes network administration, hardware maintenance, and user account administration.
3. File System Backup. System administrators or operators must conduct multiple file system backups, which can be onerously time consuming tasks. It is also expensive to duplicate backup peripherals on each server (or every few servers if slower network backup is used).
4. Price Per Seat. With only 5-10 clients per server, the cost of the server must be shared by only a small number of users. The real cost of an entry-level Unix workstation is therefore significantly greater, often as much as 140% greater, than the cost of the workstation alone.
The widening I/O gap, as well as administrative and economic considerations, demonstrates a need for higher-performance, larger-capacity Unix file servers. Conversion of a display-less workstation into a server may address disk capacity issues, but does nothing to address fundamental I/O limitations. As an NFS server, the one-time workstation must sustain 5-10 or more times the network, disk, backplane, and file system throughput than it was designed to support as a client. Adding larger disks, more network adaptors, extra primary memory, or even a faster processor do not resolve basic architectural I/O constraints; I/O throughput does not increase sufficiently.
Other prior art computer architectures, while not specifically designed as file servers, may potentially be used as such. In one such well-known architecture, a CPU, a memory unit, and two I/O processors are connected to a single bus. One of the I/O processors operates a set of disk drives, and if the architecture is to be used as a server, the other I/O processor would be connected to a network. This architecture is not optimal as a file server, however, at least because the two I/O processors cannot handle network file requests without involving the CPU. All network file requests that are received by the network I/O processor are first transmitted to the CPU, which makes appropriate requests to the disk-I/O processor for satisfaction of the network request.
In another such computer architecture, a disk controller CPU manages access to disk drives, and several other CPUs, three for example, may be clustered around the disk controller CPU. Each of the other CPUs can be connected-to its own network. The network CPUs are each connected to the disk controller CPU as well as to each other for interprocessor communication. One of the disadvantages of this computer architecture is that each CPU in the system runs its own complete operating system. Thus, network file server requests must be handled by an operating system which is also heavily loaded with facilities and processes for performing a large number of other, non file-server tasks. Additionally, the interprocessor communication is not optimized for file server type requests.
In yet another computer architecture, a plurality of CPUs, each having its own cache memory for data and instruction storage, are connected to a common bus with a system memory and a disk controller. The disk controller and each of the CPUs have direct memory access to the system memory, and one or more of the CPUs can be connected to a network. This architecture is disadvantageous as a file server because, among other things, both file data and the instructions for the CPUs reside in the same system memory. There will be instances, therefore, in which the CPUs must stop running while they wait for large blocks of file data to be transferred between system memory and the network CPU. Additionally, as with both of the previously described computer architectures, the entire operating system runs on each of the CPUs, including the network CPU.
In yet another type of computer architecture, a large number of CPUs are connected together in a hypercube topology. One of more of these CPUs can be connected to networks, while another can be connected to disk drives. This architecture is also disadvantageous as a file server because, among other things, each processor runs the entire operating system. Interprocessor communication is also not optimal for file server applications.